All species of frogs and toads have their distinct mating calls. From a deep croak to a ribbit the calls are as unique as the frogs themselves. As only the same species can mate, this makes perfect sense. Toads and frogs shut their nostrils and mouths and press air from their lungs into their vocal sacs. (1) The sac is a pouch in the throat. It blows up like a balloon. And trill, trill, croak come the night time sounds of the pond.
Toads may have a more throaty and deep call than the frogs ribbit. Both toads and frogs have sensitive ear drums called tympanum behind their eyes. They function like a regular ear with vibrations making waves through fluid and sending a signal to the brain. Frogs lungs vibrate with the calls and may be used to help locate the caller (2).
Females and Call Localization
Each female of a species is finely tuned to hear the mid-point pitch of the mating call. Some females like the deep resonant Barry Manilow voice of a bullfrog and others dig the higher alto sound of say a Choqui frog. Some frogs call as many decibels loud as a jack hammer(2). It can sound like an amphibian rock concert!
Most frogs call only during the mating season but a few will call year round. Frogs compete for how much time they get on the stage calling which turns into recognition by a female fan. Mostly only males call, but some species of female frogs will tap rhythmically like a drummer on blades of grass or plants to attract a male (3).
Frog calls are an orchestra and there is a chorus and method to their calls. Each frog gets to call in turn so that a female can hear them and choose a mate. If a frog lets out a particularly loud and long call, several other frogs will chime in to challenge him.
Frog calls are in proportion to the frogs size and this may help the female choose which mate will produce the most robust offspring. Males have much larger vocal chords than females. The spring peeper frogs vocal muscles make up 15% of its body weight as compared to only 3% in the females(4).
Female brain circuitry is different between species and from males. The need to cancel out all background noise is especially important in female frogs trying to locate their desired mate. While seeking out one frog, the female must drown out hundreds perhaps thousands of other frog calls(5). The same technique is used by manufacturers of hearing aids for humans. Research is being conducted by Dr. Feng of the University of Illinois to better hearing aids by applying this frog ability (6).
Fun Frog Fact:
A: No, the northern leopard frog calls singly. They maintain a large distance between males and have less competition for calls.